The present invention relates to an endless transport belt made of thermoresistant synthetic filaments for transporting yarn, which yarn is wound around a plurality of transport belts in the form of loops, said transport belts being arranged polygonal in cross section.
Transport belts of this type are applied in yarn conditioning plants which comprise a heat setting chamber in which, for example, carpet yarns are heat-set at temperatures nearing 200.degree. C. The temperature present in the heat setting chamber lies significantly above the necessary heat setting temperature. In order to ensure that the heat setting temperature is reached even at difficult points along the yarn, the heat setting chambers have, over the years, become longer and longer. In U.S. Pat. No. 5,557,862, for example, in which transport belts of the above mentioned type are used, a length of the heat setting chamber of 5 m is disclosed. As the transport belts extend over longer areas upstream and downstream of the heat setting chamber, and in addition, circulate, the belts can reach lengths of up to 20 m.
As a result of the polygonal arrangement of, for example, four transport belts, around which the yarns are wound in the form of loops before they enter the heat setting chamber, the belts experience a high tension load. Thus the transport belts, in particular in the case of long heat setting chambers, are stretched to an extent that is detrimental to the operation of the yarn conditioning plant.
It is an object of the present invention to create an endless transport belt for application in the above mentioned case, which transport belt is able to cope with the high tension load and whose stretch rate lies below 1%.
This object has been achieved in accordance with the present invention in that at least one reinforced thread is added to the synthetic filaments in order to reduce the stretching of the transport belt, the modulus of elasticity of the reinforced thread being only slightly lower than that of steel.
Transport belts usually used in the industry are made of chemical fibres, for example aramide fibre composites, which belts have a round cross section of approximately 7 mm. In the case of the present invention, one or more reinforced threads, for example four in the form of steel wires or cords, are added to the chemical fibre composites, which influence the stretch tendency of the entire transport belt in such a positive way that the entire extent of the stretch remains below 1%, even at high temperature loads. The reinforced thread may consist of an aramide fibre composite comprising stainless steel fibres.
The low-stretch, thermoresistant transport belts must have a suitable surface structure for transporting yarns. The surface must, on the one hand, be sufficiently smooth, so that the yarns are not damaged, while on the other hand, they must have sufficient friction for the required yarn transport. When the reinforced thread is a steel one, then it should be located in the interior of the transport belt and in no case on its surface. Furthermore, the steel thread must, of course, be made of stainless steel. Due to the additional bending load which occurs when the transport belt turns around, the steel thread experiences a constant alternating load, which can easily mean ten million load alternations during its lifetime. The reinforced thread must be able to withstand this load. In order that the belt material can be made into an endless transport belt, both ends must be capable of being spliced together in such a way that the diameter of the transport belt does not alter at the splice point and that the necessary tensile strength is transferred to the splice point.
The transport belt according to the present invention can be produced in a variety of ways, for example as an endless plaited belt by means of loops plaited over one another, or by means of stranding, whereby a cladding is wound around a core. In a preferred embodiment of the present invention, a clad-core-plait is provided for the transport belt, whose plaited form of the cladding, as well as of the core, permits splicing. For a reinforced thread, at least one wire cord made of Niro wire filaments is preferably worked into the core plait, which can be a cross or loop plait. Two to twenty four steel threads are possible, depending on the plaiting.
In the case of a clad-core transport belt having a circular or quadratic cross section, which is plaited from a plurality of wire threads and a plurality of synthetic filaments, the core is plaited from fibres having a high friction coefficient, whereby in a preferably even number of strands, one or a plurality of wire threads is stranded or plaited in long lay or in reverse lay with the fibres towards the strand.
Alternatively, it is possible that the reinforced thread or threads are entire braided layers, which are applied between the core and the braided cladding.
The present invention achieves the aim of creating a friction and a form closure also at the ends, joined together by splicing, by means of the combination of chemical fibres with a high friction coefficient, and the reinforced thread, preferably in the form of a fine wire, so that without a direct connection of the reinforced fibres, a longitudinal stability arises even at high temperatures and under load.